Field of the Invention
The invention relates to a turning device for a printing press, in particular, a sheet-fed offset printing press, having a transfer device disposed between an impression cylinder of a printing unit located upline of the transfer device and an impression cylinder of a printing unit located downline of the transfer device, the transfer device including a first gripper device for accepting a sheet from the impression cylinder of the upline printing unit and including a second gripper device for gripping a trailing edge of the sheet and transferring it to the impression cylinder of the downline printing unit.
For printing both sides of sheetlike material in a sheet-fed offset printing press for perfecting or perfecter printing, i.e., recto and verso printing, after the upper side of the sheet has been printed, it is necessary for the sheet to be turned over by a turning device so that the sheet can then be printed on the rear side thereof.
From the German Published, Non-Prosecuted Patent Application DE-OS 41 26 643, a sheet guiding cylinder for a printing press has become known that has a circumferential surface with many suction bores formed therein, whereon the sheet is held by suction and is smoothed.
In the published German Patent Document DE 37 10 257 C2, there is disclosed a turning device with a storage drum disposed between an upline impression cylinder and a downline impression cylinder, a sheet to be turned being held at a leading edge thereof by a gripper device and at a trailing edge thereof by suction devices on the circumferential surface of the storage drum, a tongs-type gripper device of the downline impression cylinder gripping the trailing edge of the sheet after the latter has passed through gripper central areas between the storage drum and the downline impression cylinder, and has conducted the sheet to a downline printing gap or nip.
In German Patent 30 50 295, a turning device is disclosed wherein a sheet, with its leading edge first, is transferred from an upline impression cylinder to a first gripper device of a transfer drum, the trailing edge of the sheet being held by suction from a suction device against the circumferential surface of the transfer drum, and the trailing edge of the sheet is gripped by a tongs-type turning gripper system, even before the first gripper device releases the leading edge of the sheet. The sheet is then transported, with its leading edge leading, to a suction belt which extends in a curved manner and guides the sheet. Thereafter, the sheet is transferred by its trailing edge from the tongs-type turning gripper device to a downline impression cylinder.